Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session R37: Drops: General |
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Chair: William Ristenpart, University of California Davis Room: Portland Ballroom 252 |
Tuesday, November 22, 2016 1:30PM - 1:43PM |
R37.00001: A parametric study on the rise of a pair of bubbles using algebraic volume of fluid method: effect of diameter and viscosity ratio. Amaresh Dalal, Amol C Kulkarni, Jai Manik, Ganesh Natarajan The effect of droplet diameter and viscosity ratio on the coalescence of two bubbles rising in a quiescent liquid has been studied numerically using algebraic volume of fluid (VOF) method. If the upper bubble diameter is 75 {\%} of the lower bubble, the time taken for their coalescence increases in comparison with the case of equal bubble diameter. For the case, when the diameter of the upper bubble is reduced, this delay may be attributed to comparatively weaker jet formed behind the leading bubble, ultimately resulting in lesser acceleration of the trailing bubble. While for the other case, when the diameter of the lower bubble is reduced, it is because of a totally different scenario of liquid entrapment observed during coalescence. The effect of viscosity of the surrounding fluid is also noticed separately for the situation when the diameters of the bubbles are equal. It has been observed that, the increase in viscosity of the surrounding fluid will increase the form drag over the bubbles, eventually leading to the delay in their coalescence. [Preview Abstract] |
Tuesday, November 22, 2016 1:43PM - 1:56PM |
R37.00002: Charged Water Droplets can Melt Metallic Electrodes Eric Elton, Ethan Rosenberg, William Ristenpart A water drop, when immersed in an insulating fluid, acquires charge when it contacts an energized electrode. Provided the electric field is strong enough, the drop will move away to the opposite electrode, acquire the opposite charge, and repeat the process, effectively `bouncing' back and forth between the electrodes. A key implicit assumption, dating back to Maxwell, has been that the electrode remains unaltered by the charging process. Here we demonstrate that the electrode is physically deformed during each charge transfer event with an individual water droplet or other conducting object. We used optical, electron, and atomic force microscopy to characterize a variety of different metallic electrodes before and after drops were electrically bounced on them. Although the electrodes appear unchanged to the naked eye, the microscopy reveals that each charge transfer event yielded a crater approximately 1 micron wide and 50 nm deep, with the exact dimensions proportional to the applied field strength. We present evidence that the craters are formed by localized melting of the electrodes via Joule heating in the metal and concurrent dielectric breakdown of the surrounding fluid, suggesting that the electrode locally achieves temperatures exceeding 3400$^\circ$C. [Preview Abstract] |
Tuesday, November 22, 2016 1:56PM - 2:09PM |
R37.00003: Direct cascade of droplet fragmentation in sparkling fireworks Chihiro Inoue, Emmanuel Villermaux Sparkling fireworks are popular in Japan for 400 years. They are made by a twisted paper simply wrapping 0.1g of black powder at the lower end. Ignited there, the powder melts in a fireball of molten salts, ejecting droplets seen as light streaks. The droplets successively fragment up to eight times leading to ever-smaller size and their branched light streaks traces are similar to pine needles. The phenomenon involves chemical reactions, thermal decomposition of metastable compounds, gas bubble nucleation and bursting, the formation of liquid ligaments, and droplets. We depict the features of this unique direct fragmentation cascade in nature, where thermal diffusion inside each droplet determines its lifetime. Droplet radius getting exponentially smaller until thermal production and heat losses equilibrate. We compute and document experimentally the number of fragmentation steps, and the overall size of the light streaks as well. [Preview Abstract] |
Tuesday, November 22, 2016 2:09PM - 2:22PM |
R37.00004: ABSTRACT WITHDRAWN |
Tuesday, November 22, 2016 2:22PM - 2:35PM |
R37.00005: ABSTRACT WITHDRAWN |
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